Closed-Loop UV-Activated Solvent-Based PFCAs Defluorination and Adsorbent Regeneration

Granular activated carbon (GAC) adsorption is the most widely used method for removing per- and polyfluoroalkyl substances (PFAS). Thermal regeneration of spent GAC is currently preferred over solvent-based methods because regenerating both solvents and GAC while preserving the adsorbent performance remains a significant challenge. Here, we proposed an innovative “extract-and-degrade” strategy in which organic solvents, used as GAC extractants, are directly exposed to UV 254 nm irradiation, allowing effective defluorination under mild conditions while simultaneously allowing solvent recycling. Among 18 tested solvents, the aprotic solvent acetonitrile (ACN) resulted in complete PFOA degradation and >70% defluorination within 24 h under UV irradiation. This performance is attributed to the activation of PFOA molecules induced by ACN’s high polarity, which facilitates electron transfer from the negatively charged −C≡N group of ACN to the positively charged −OH group of PFOA. Studies on perfluorocarboxylic acids (PFCAs) with different chain lengths revealed that longer chains are more prone to electron capture for subsequent degradation steps, consistent with their adiabatic electron affinity (AEA) values. Finally, both GAC and ACN demonstrated excellent stability and reusability in cyclic tests. This work sheds light on previously unexplored photochemistry in nonaqueous media and highlights the potential of organic solvents as recyclable platforms for PFCAs defluorination and adsorbent regeneration in water purification systems.